Traditionally, a large number of particulate matters are used individually or in different combinations as adsorbents in water filtration system, air pollutant trapping systems, sewerage treatment plants, to name a few. This particulate matters include activated carbon, metal-organic framework, carbon nanotube, biochar, iron oxide, alumina, titania, zirconia, tin oxide, graphene, beta-cyclodextrin, calixarenes, manganese oxide, poly(styrene-divinyl benzene), carboxen, fullerene, cation exchange resins, anion exchange resins, and zwitterionic resins. These particulate matters offer a large variety of intermolecular interactions towards analytes via μ-μ stacking interactions, cation-μ bonding interactions, electron donor-acceptor interactions, hydrophobic interactions, hydrogen bonding interaction, cation exchange, anion exchange, and dipole-dipole interactions depending on their functional characteristics. Advantageously, many of these particulate matters possess extremely high surface area but disadvantageously demonstrate a strong tendency to form agglomeration. In their pristine form, aggregation excludes a large portion of these particles' available surface area to analytes that by intermolecular and/or ionic interactions undergo adsorption onto the surface of the particulate matters. As a result, the adsorption capacities of many of these particulate materials remain largely unexploited in practical applications.
Surface-bonded inorganic/hybrid organic-inorganic polymer coatings and monolithic beds are popular sorbents. These systems display high chemical stability and offer a diverse array of extracting phases for solvent-free/solvent minimized analytical sample preparation. The availability of a wide variety of sol-gel precursors and sol-gel active organic polymers allow facile synthesis of advanced material systems with unique selectivity, enhanced extraction sensitivity and high thermal, mechanical and solvent stability. This sol-gel derived inorganic/hybrid organic-inorganic advanced material system have been shown to be effective in solvent free/solvent minimized sample preparation for a wide variety of analytes with biological, environmental, clinical, toxicological, food, pharmaceutical, bio-analytical, and forensic significance.
Sol-gel technology is adaptable to forming multi-component materials that have customized surface morphologies, selectivities and affinities of the sorbent. A wide variety of sol-gel silica, titania, zirconia, alumina, and germania-based precursors are commercially available. Additionally, a wide range of sol-gel reactive organic ligands are available to design inorganic/hybrid organic-inorganic sol-gel coatings or monolithic beds that can be used to target a particular analyte or sample matrix with improved selectivity, sensitivity, extraction phase stability and performance.
To this end a carbonaceous or non-carbonaceous particulate matter encapsulated in sol-gel sorbent matrix has the potential to provide selective and efficient sorbents. The encapsulation of particulate matters in sol-gel inorganic matrix successfully prevents their agglomeration; on the other hand, the encapsulation of particulate matters in sol-gel hybrid organic-inorganic matrix synergistically extends the affinity and selectivity of the composite sorbent towards the target analyte(s). Such effect can't be achieved by using only the pristine particulate matters, sol-gel inorganic matrix (e.g., sol-gel silica) or sol-gel hybrid organic-inorganic (sol-gel silica bonded to organic polymer) matrix.